1. Field of the Invention
The invention relates generally to the field of substance and material detection, inspection, and classification, and more particularly to an electronic scanning detection system (e.g., a fluorescence spectrograph) with a high degree of specificity and accuracy, operating in the ultraviolet portion of the electromagnetic spectrum which is used to identify specific individual and unique mixtures of substances including, for example, medications and alcohol products.
2. Discussion of the Related Art
Ultraviolet (“UV”) fluorescence spectroscopy is an analytical technique used to identify and characterize chemical and biological materials and compositions. In operation, UV fluorescence systems direct energy (in the form of concentrated photons) from an excitation source toward a target area using, for example, reflective and/or refractive optics. Photoelectric interactions of the photons with the sample material produce detectable wavelength-shifted emissions that are typically at longer wavelengths (toward the visible) than the absorbed excitation ultraviolet photons.
The wavelength shift is due to an energy transfer from the incident photons (at an appropriate wavelength) to the target materials. The transferred energy causes some of the sample's electrons to either break free or enter an excited (i.e., higher) energy state. Thus, these excited electrons occupy unique energy environments that differ for each particular molecular species being examined. As a result, electrons from higher energy orbital states “drop down” and fill orbitals vacated by the excited electrons. The energy lost by the electrons going from higher energy states to lower energy states results in an emission spectra unique to each substance. When this process occurs in a short time, usually 100 nanoseconds or less, the resultant photon flux is referred to as fluorescence.
The resultant emission spectrum generated is detected with an ultraviolet spectrograph, digitized and analyzed (i.e., wavelength discrimination). Each different substance within the target area produces a unique spectrum that can be sorted and stored for comparison during subsequent analyses of known or unknown materials.
UV fluorescence spectroscopy does have some drawbacks. First, it can be affected by interference (or clutter). Interference is defined as unwanted UV flux reaching the detector that does not contribute directly to the identification of a material of interest. For example, when attempting to detect illegal substance on clothing, clutter can arise from exciting unimportant molecules in the target area, exciting materials close to the detector/emitter region, external flux from outside the target area (including external light sources) and scattering from air and/or dust in the light path. Thus, one goal of the invention is enabling efficient and accurate discrimination between all these and other sources of interference in conjunction with an appropriate analysis system (using specific algorithms and spectral filtering).
UV fluorescence systems are also limited in terms of sensitivity distances. Greater distances between the substance of interest and the UV excitation source and detector result in weaker return photon flux (i.e., weaker, if any, fluorescence) from the sample material. Factors influencing the range and sensitivity include integration time, receiving optics aperture, source power and the characteristics of the path through which the ultraviolet light travels.
Conventional spectroscopy and detection techniques include, among other things, neutron activation analysis, ultraviolet absorption, ion mobility spectroscopy, scattering analysis, nuclear resonance fluorescence, quadrupole resonance and various chemical sensors. Each of these methodologies, however, suffers from deficiencies. For example, neutron activation analyses, while capable of directly measuring ratios of atomic constituents (e.g., hydrogen, oxygen, nitrogen, and carbon) require large energy sources (such as accelerators) that have high power demands. Traditional UV absorption and scattering techniques are subject to high degrees of inaccuracy (i.e., false alarms and omissions) absent sizeable reference resources and effective predictive analysis system. Scattering analysis techniques suffer similar shortcomings.
Ion mobility spectroscopy devices are currently in use at many airports for “wiping” analysis, but suffer from low sensitivities and have high maintenance demands. Resonance fluorescence is an emerging and promising technology, but requires a large, complex energy source for operation. Quadrupole resonance techniques offer a good balance of portability and accuracy, but are only effective for a limited number of materials (i.e., they have an extremely small range of materials they can reliably and accurately detect). Finally, chemical sensors, while very accurate, are slow acting and have limited ranges. Furthermore, chemical sensors do not always produce consistent results under varying environmental conditions (e.g., high humidity and modest air currents).